Touch Sensor Controller Negative Voltage Drive Signal
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Solution Overview
Problem
Existing touch sensor panel controllers face challenges in enhancing detection sensitivity, particularly in portable devices where noise interference affects the accurate detection of small capacitance changes caused by finger or hand contact, and there is a need to improve the signal-to-noise ratio in conjunction with display driving.
Innovation Solution
The implementation of a touch sensor panel controller that applies an AC drive signal with a negative voltage level to the Y electrodes, synchronizes charge pump operations with multiple clock phases, and adjusts the timing of drive waveforms to minimize noise interference from display panel voltage changes, thereby increasing detection sensitivity and signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AC drive signals with positive voltage levels are used for touch sensor panels, then the circuit design is simpler, but the detection sensitivity and signal-to-noise ratio deteriorate due to noise interference from display panel voltage changes
Solution Approach 1:
The patent changes the voltage level parameter of the AC drive signal from conventional positive voltage to negative voltage. Specifically, the drive signal swings between a negative voltage level (e.g., -3.3V to -15V) and a reference voltage (e.g., 0V or ground). This parameter change shifts the operating point away from the noisy display voltage transitions, thereby improving detection sensitivity and signal-to-noise ratio without requiring fundamentally new circuit topologies.
2Reliability
If the touch sensor drive waveforms are synchronized with display drive waveforms, then the system operation is coordinated, but noise interference from display voltage changes affects touch detection accuracy
Solution Approach 1:
The patent applies preliminary anti-action by intentionally desynchronizing the touch sensor drive waveforms from the display drive waveforms. The touch controller is configured to activate its drive electrodes at different times than when the display panel switches voltages. This timing offset prevents the display voltage transitions from coupling noise into the sensitive touch detection circuits, thereby protecting touch detection accuracy while maintaining overall system coordination.
Solution Approach 2:
The patent employs periodic action by using AC-coupled drive signals with specific frequencies and duty cycles for the touch sensor electrodes. The drive electrodes are activated in alternating periods (e.g., during horizontal blanking intervals or specific scan periods) rather than continuously, and the frequency is chosen to avoid interference with display refresh rates. This periodic activation pattern, combined with negative voltage levels, creates a rhythm that is inherently more resistant to display-induced noise.
3Measurement precision
If AC pulse driving is used to charge intersection capacitances, then touch signals can be detected, but the small capacitance change (at most 1pF) is difficult to judge correctly due to surrounding noise
Solution Approach 1:
The patent extracts the touch detection operation from the noisy display driving environment by using separate, desynchronized timing. The touch controller independently manages its drive electrode activation timing, extracting it from the display's voltage transition periods. Additionally, the negative voltage AC drive signal extracts the touch detection bandwidth away from the display noise spectrum, effectively separating the weak capacitance change signal (at most 1pF) from surrounding noise sources.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of AC coupling capacitors and negative voltage level shifting circuits between the touch sensor electrodes and the detection amplifiers. These intermediary elements block DC offset voltages and high-frequency noise from the display while allowing the AC touch signal to pass through. The negative voltage level acts as an intermediary reference that isolates the sensitive capacitance measurement from the noisy display voltage domain.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the detection sensitivity and signal-to-noise ratio, allowing for more accurate touch detection while avoiding degradation of display performance by synchronizing the touch sensor panel controller with the display driver's operations.
Implementation Method 1
a touch sensor panel supporting multiple points of touching according to a mutual capacitance method has Y electrodes used as drive electrodes and X electrodes used as detection electrodes, in which the X and Y electrodes are crossing each other at right angles with dielectric interposed therebetween, and capacitance (i.e. intersection capacitance) is formed at each intersection
Data Source
AI summary
Provided is a touch sensor panel which can increase the detection sensitivity of a touch relatively readily. The touch sensor panel controller supplies drive electrodes of a touch sensor panel with a high-voltage AC drive signal with its low level set to a negative voltage and drives them. The time of change of a drive waveform supplied to the drive electrodes of the touch sensor panel is shifted relative to the time of change of a drive waveform supplied to a display scan electrode. The touch sensor panel controller uses a charge pump in synchronization with clock signals of more than one phase to produce a high drive voltage to activate drive electrodes of the touch sensor panel, and the clock signals of more than one phase are initialized each time the drive electrode is subjected to AC pulse driving.